We analyze two-neutron transfers in nuclei within a mean-field approach. We first show that the response associated with pairing excitations can be affected by the surface/volume localization of the employed effective pairing interaction. Then, ground-state-to-ground-state transitions are studied and some improvements on the currently used theoretical formulas are discussed. Finally, Cr isotopes at the drip line are analyzed. The analysis of pair-transfer reactions in these nuclei may improve our understanding of two aspects: the spatial distibution of pairing correlations in nuclei and the debated question of the persistence of pairing at the drip lines.